Electron Cyclotron stray radiation detector studies for JT-60SA

Abstract

Most of the present and future magnetic fusion devices rely on high power mm-waves injection for a variety of applications like plasma breakdown, heating and control. Since under specific operating conditions the mm-waves might not be fully absorbed, potentially damaging in-vessel components, the detection of the non-absorbed radiation is recommended. Among the options for stray radiation detection, we consider here the possibility to exploit the solid body bolometer and its use for JT-60SA. Analysis of the residual power fraction expected for low absorption plasma conditions is presented, considering the dependence on the Electron Cyclotron Resonance Heating (ECRH) system and plasma parameters of JT-60SA. The residual power hitting the wall is evaluated looking at direct illumination and cross-polarization effects. The possibility to integrate a sensor for EC stray radiation, adapting the solution of the detector developed for ITER, is the main outcome of this study. In the ITER bolometer the differential thermocouple principle is considered to single out the nuclear heating and the microwave loads. A key component of the detector is the metal body with a ceramic coating layer, optimized for 170 GHz and 60 GHz. Mm-waves characterization of different coating samples has been performed to identify the optimal solution for JT-60SA considering its multi-frequency ECRH system (138 GHz, 110 GHz, 82 GHz), and will be here presented. The experience from JT-60SA equipped with these sensors will be also useful for their future use in ITER.